When using "new" to initialize unique_ptr

Smart Pointers are a new concept for me. I have been trying to wrap a File class around fopen_s and fclose using a smart pointer with a custom deleter (unique_ptr).

Below is my attempt. It successfully compiles, runs, and generates a file named "text.txt" with the contents "Hello World" as expected.

I had to use "new" to initialize unique_ptr in my Open function since make_unique does not appear work with custom deleters. Since I am using "new" is my custom deleter responsible for freeing that allocated memory?

I have stepped through my program (VS2019). File::Close only gets called once. I expected it to be called when "handle" in my File:Open function went out of scope, but this was not the case. This behavior may be influenced by the call to std::move(). Not sure how to investigate further on what happens here.

#include <Windows.h>
#include <memory>
#include <string>
#include <map>

class File
{

private:

//functors - custom deleter
  struct Close { void operator()(FILE** _handle); };

//type definitions
  typedef std::unique_ptr<FILE*,File::Close> Handle;
  typedef std::map<std::string,Handle> HandleMap;

//static members
  static Handle& Open(std::string _name, std::string _mode);
  static HandleMap s_handle_map_;

//variables
  Handle& handle_;
  std::string name_;

public:

//functions
  File(std::string _name, std::string _mode);
  void Write(std::string _message);

};

File::HandleMap File::s_handle_map_;

File::File(std::string _name, std::string _mode)
:handle_(Open(_name,_mode)),
 name_(_name)
{
}

File::Handle& File::Open(std::string _name, std::string _mode)
{
  bool exist = s_handle_map_.count(_name) > 0;

  if (!exist)
  {
    Handle handle(new FILE*(nullptr));

    //open new file
    fopen_s(
      handle.get(),
      _name.c_str(),
      _mode.c_str()
    );

    //transfer ownership of handle
    s_handle_map_.emplace(
      _name,
      std::move(handle)
    );

  }

  return s_handle_map_[_name];
}

void File::Close::operator()(FILE** _handle)
{
  fclose(*_handle);
  *_handle = nullptr;

  //necessary?
  delete _handle;
  _handle = nullptr;
}

void File::Write(std::string _message)
{
  fprintf(*handle_, _message.c_str());
}

int WINAPI WinMain(HINSTANCE _instance, HINSTANCE _previous, LPSTR _cmd, int _show)
{
  File file("test.txt","w");
  file.Write("Hello World\n");
  return 0;
}